This application claims the priority of German application 199 01 147.8, filed in Germany on Jan. 14, 1999, the disclosure(s) of which is (are) expressly incorporated by reference herein.
The present invention relates to a yarn withdrawal nozzle for an open-end rotor spinning apparatus having a short funnel-shaped yarn deflecting surface, which begins at a plane front surface and graduates into a yarn withdrawal channel.
Open-end rotor spinning apparatus run today at spinning rotor speeds of 130,000 rpm and more. In the processing of synthetic fibers, in particular polyester fibers, or of mixtures of natural and synthetic fibers, the operating speeds are, however, limited. This is because heat damage caused by frictional heat occurs in the synthetic fibers. This damage caused by overheating is particularly noticeable at the yarn withdrawal nozzle, as the spun yarn rotates crank-like at high speeds there and is pressed onto the yarn deflecting surface of the yarn withdrawal nozzle.
Many ideas as to how to reduce overheating at the yarn withdrawal nozzle have already been tried and tested.
German published patent 24 10 940 suggests directing a cooling air stream onto a yarn guiding funnel, which is similar to a yarn withdrawal nozzle. Here the cooling air stream is the outside surrounding air which penetrates into the inside of the rotor spinning apparatus. This idea was never put into commercial practice.
In U.S. Pat. No. 3,930,356, it is suggested that conditioned air be used as transport air for the fibers transported from the opening device to the spinning rotor, and that this conditioned air be used to cool the yarn delivery area. The frictional heat generated by the thread is thus presumed to be drawn off. Again, this idea was never put into commercial practice.
According to a further idea in U.S. Pat. No. 5,666,799, it is intended that the yarn withdrawal nozzle is cooled by designing a double-walled channel plate, to which the yarn withdrawal nozzle is applied. The arising free space is then connected to a coolant loop. This design is very complicated and was never put into commercial practice.
A yarn withdrawal nozzle is described in U.S. Pat. No. 5,265,406, in which a material having high heat conducting properties is inserted between the wear-resistant, yarn deflecting surfaces and a take-up of the yarn withdrawal nozzle. 5 The heat from the yarn-guiding surfaces is thus presumed to be quickly drawn off. As the yarn-guiding surfaces are not good heat conductors, practically no rapid drawing off of heat occurs in any case at those points where overheating really occurs.
According to U.S. Pat. No. 5,321,943, it is therefore provided that the yarn-guiding surfaces of a yarn withdrawal nozzle are made from a wear-resistant material having high heat-conducting properties, for example titanium diboride. It has been shown, however, that the chosen material does not necessarily possess good spinning properties.
Finally, according to German published patent 32 39 289, the yarn, deflected at the yarn withdrawal nozzle, exerts a surface pressure only on a contact surface which is curved, like an arc of a circle, in axial cross section, which contact surface is, in comparison to other yarn withdrawal nozzles, relatively short. The contact surface is deliberately shortened in that the beginning of the arc, for which a radius of 4 mm is given, is cut off by a secant. The aim of these measures is to reduce the axial forces of the withdrawn yarn. The contact surface begins with a clearly defined edge, at which the yarn drawn off from the spinning rotor comes into contact with the yarn withdrawal nozzle for the first time. There is no reference to the reduction of heat damage in this publication.
It is an object of the present invention to design the simplest yarn withdrawal nozzle possible with which synthetic fibers can be spun at higher speeds than before without resorting to additional complicated measures.
This object has been achieved in accordance with the present invention in that the radius of curvature measures a maximum of 3 mm and that the front surface takes the form of a surface tangential to the yarn deflecting surface.
It has surprisingly been shown that, by means of the significant reduction in the radius of curvature in comparison to known yarn withdrawal nozzles, heat damage in the case of synthetic fibers, in particular polyester fibers, can be reduced. It has been shown that spinning can take place at approximately 15% higher speed and thus with 15% higher delivery than if a previously standard radius of curvature, in the range of 6 mm and more, is used. In spite of the increased surface pressure caused by the small radius of curvature, the desired effect occurs probably because the yarn deflecting surface is extremely short, so that the deflected yarn leaves the yarn deflecting surface again before any heat damage can occur. Because the front surface takes the form of a tangential surface to the yarn deflecting surface, the yarn drawn off from the spinning rotor does not come into contact with an edge. The front surface is practically exempted from any surface pressure, but forms for the yarn a kind of supporting guiding surface.
The yarn deflecting surface graduates advantageously without a distinct edge continuously into a hollow cylindrical part of the yarn withdrawal channel. Thus additional increased surface pressure caused by any deflecting edges is avoided.
For reasons of technical production, it is purposeful when the radius of curvature of the yarn deflecting surface is constant throughout.
The outer diameter of the front surface is limited to only what is absolutely necessary, and measures advantageously a maximum of 10 mm. In order to reduce friction, the yarn deflecting surface and the front surface are both polished smooth. The front surface graduates advantageously at the outer diameter into a conical ring surface, with which the yarn does not come into contact, that is, which is staggered in relation to the yarn running plane.
It can be additionally provided that the yarn deflecting surface is provided in a known way with notches. Thus the false twist, which occurs at the yarn deflecting surface, is periodically interrupted, so that the generated false twist can "jump back" so to speak from time to time.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.